Roller type conveyor apparatus is commonly utilized for handling heavy items, for example installing and removing large lead-acid storage batteries, such as those used in warehouse forklift trucks, to and from their host vehicle for regular recharging purposes. In conventional heavy duty conveyors, the rollers, bearings and shafts are made from metal, typically steel. When metallic conveyors are utilized for battery handling there are two potential problems:
(A) there may be electrical leakage currents from metal battery housings to the metal rollers, and PA1 (B) acid or other corrosives spilling and/or leaking from the batteries tend to corrode the metal rollers and leach to the metal bearings, causing them to seize.
In one known approach to corrosion resistance a sheath of plastic such as 1/4" thick PVC (polyvinyl chloride) is added over a metal roller. In another approach the entire roller may be made non-metallic and attached concentrically around a rotatable steel shaft in the manner of a washing machine roller. Such approaches provide electrical insulation to remedy problem (A); however, with metal-to-metal bearing surfaces, problem (B) remains since it is likely that leaching of corrosive fluids will damage and eventually destroy the bearings.
The use of a non-metallic material such as plastic throughout would solve both problems (A) and (B); however, no practical plastic material is known to provide suitable low bearing surface friction and long bearing life in a plastic-to-plastic bearing interface while also providing a suitable resilient roller surface along with the required ultimate overall strength, especially in the shaft.